There's a long thread on the Ayatana mailing list about the upper-left Ubuntu button in the upcoming Ubuntu 11.04. Currently, this button will open Dash. But there are also two shortcuts in the launcher which trigger Dash (Applications / Files Places) which make the Ubuntu button redundant - this lead to some new ideas for the upper-left Ubuntu button behavior.

One very interesting idea was posted by Marc Lajoie and he calls it "two-sided dock". Here's how it's supposed to work in Marc Lajoie own words:

On one side, the application buttons, on the other, the "function" buttons. The Ubuntu button would flip the dock over (perhaps with a pretty revolving animation!).

Of course, if the dock is hidden, the first click will recall it. The second click will flip the dock.

He also adds:

The dock could be recalled immediately when hovering over the button, saving the extra click when using a mouse, so that to get to the "places" side of the dock only one click would be necessary.